The present disclosure relates to a valve control device and a valve control method that control the opening degree of a valve provided in the intake passage of an engine, the exhaust passage of an engine, or a passage connected to one of the intake passage and the exhaust passage.
The engine draws in working gas in an intake stroke and supplies the drawn working gas with fuel, thereby generating air-fuel mixtures. Thus, the properties of the working gas drawn into the engine are remarkably important for controlling the output or exhaust gas of the engine. Japanese Laid-Open Patent Publication No. 2003-193875 describes an example of a device that is mounted in an engine system and controls the properties of such working gas. More specifically, the device includes an exhaust gas recirculation (EGR) device having an EGR passage, through which some exhaust gas flows back from the exhaust side toward the intake side, a turbocharger that turbocharges intake air using the energy of exhaust gas, and the like.
Each of the EGR device and the turbocharger includes a valve capable of varying the cross-sectional flow areas of passages through which various types of gases flow. That is, the EGR device includes an EGR valve capable of varying the cross-sectional flow area of an EGR passage, and the turbocharger includes a variable nozzle (variable valve) capable of varying the cross-sectional flow area of a passage through which exhaust gas flows into the turbine. The opening degrees of these valves may need to be controlled so that the properties of working gas drawn into the engine are highly precisely controlled to be desired properties. Such control may be needed not only for the valves including the EGR device and the turbocharger but also for a valve that is provided in the intake passage of the engine, the exhaust passage of the engine, or a passage connected to one of the intake passage and the exhaust passage and can adjust the cross-sectional flow area of the passage.